1. Field of the Invention
The present invention relates to a motorized wheeled chassis having a pair of independently pivotable drivewheels and, in particular, to a motorized wheelchair having independently pivotable offset drivewheels, thus enabling true and efficient multidirectional travel.
2. Description of the Related Art
A conventional motorized wheelchair is typically equipped with a chassis having front wheels that consist of a pair of free-spinning castors and rear wheels that consist of a pair of motor-operated wheels which are fixed to the chassis and are frequently driven independently of one another by reversible, variable-speed DC motors. In such wheelchairs, the rotative direction and speed of each of the right and left motor-operated wheels are varied by reversing the power source connection of the appropriate DC drive motor and by regulating the input voltages to the motor, which actions result respectively in switching the direction of movement of the wheelchair (between forward and backward travel) and changing the speed (RPM) of movement of the wheelchair on or along an underlying ground surface. In this manner, a conventional motorized wheelchair is fairly easily advanced, retreated, turned to the right or to the left, and rotated in a stopped state.
However, such a conventional motorized wheelchair cannot be moved laterally with the rider remaining face forward because the motor-operated wheels cannot be pivoted so that they are directed sideways with respect to the rider. This restriction in movement interferes with the rider""s ability to utilize the wheelchair completely, to move with total freedom of motion, and to perform certain functions that would be available only through lateral motion as, for example, painting on a horizontally-elongated surface or writing on a blackboard. Moreover, currently known drive wheel control arrangements further restrict the range of wheelchair movements in additional ways and may thereby limit a user""s flexibility of motion along particular paths or directions of travel.
In order to solve the problems related to conventional motorized wheelchairs, the inventor of the invention described in this disclosure invented a xe2x80x9cWheeled Chassis Having Independently Pivotable Drivewheels for Omnidirectional Motionxe2x80x9d, described in U.S. Pat. No. 5,547,038 (hereinafter referred to as the ""038 wheelchair), the entire disclosure of which is incorporated herein by reference. The ""038 wheelchair not only allows the rider to face forward while moving laterally, but also provides a minimal turn radius for rotating while remaining in one location.
As shown in FIG. 1, the chassis 1 of the ""038 wheelchair has a generally rectangular frame 2 with four wheels, one disposed in each corner. In what shall be referred to as the front of the chassis 1, two wheels, each labeled 4, are attached to the frame 2 by a shaft 10 that extends along an axis defined generally normal or perpendicular to the ground surface and each links to a bearing assembly 12. Assembly 12, at its lower portion, connects to a hub 14 of wheel 4. By this construction, two independently pivoting, free-spinning wheels 4 are positioned at the front of chassis 1.
The two wheels at the rear of chassis 1 are the left drivewheel 6(a) and the right drivewheel 6(b). Each drivewheel 6 is attached by a kingpin 16 to frame 2. Each kingpin 16 at its upward end passes through a channel 18 in frame 2 containing a bearing assembly to provide freedom of selectively controlled pivotal rotation about an axis defined substantially normal to the supporting ground surface. The top end of each kingpin 16 protrudes beyond the top surface of frame 2 and has rigidly connected thereto a drive gear 22 for engagement with a rotative mechanism (not shown). Thus, drivewheel 6(a) may pivotally rotate around substantially vertical axis 23 and drivewheel 6(b) may pivotally rotate around a substantially vertical axis 24.
The lower portion of each kingpin 16 is rigidly attached to a drivewheel assembly 20 which comprises a variable speed, bidirectional drive motor 8 that rotatably drives the respective drivewheel 6 in a forward or reverse direction. There is no linkage or attachment of the two separate motor drives 8, and coordination between the two is implemented by a control system (not shown).
With the construction shown in FIG. 1, each drivewheel 6 is capable of being pivotally rotated in a complete 360xc2x0 circle without interference or impediment. Some of the varieties of motion possible with such a construction are shown in FIGS. 2A-2C. In FIG. 2A, the two rear drivewheels 6 are shown in two different positions (FIG. 2A1 and 2A2). In FIG. 2A1, the drivewheels 6 are in a straight (0xc2x0) position allowing the wheelchair to be moved straight forward or straight backward. In FIG. 2A2, the two drivewheels 6 are positioned for a minimum radius turning circle. To get to the minimum circle position from the straight position, the right drivewheel 6(b) rotates 45xc2x0 clockwise and the left drivewheel 6(a) rotates 45xc2x0 counter-clockwise. In this rotated position, the wheelchair can turn or rotate in place.
It should be noted that the 45xc2x0 rotation position only applies to a wheeled chassis with a square frame, i.e. with equal length and width, or in which the wheels are mounted at equal front-to-back and side-to-side distances apart. In general, the wheel position for rotation is perpendicular to the diagonal of the chassis frame. As an example, the angle of the rotation position for a frame whose length is longer than its width would be more than 45xc2x0. Hereinbelow, although the specification discusses rotation angles such as 45xc2x0, 90xc2x0, etc., it should be understood that 45xc2x0, 90xc2x0, etc. are only exemplary rotation angles that are appropriate for a square frame, and the present invention applies to any roughly rectangular frame where the appropriate rotation angles for the different positions may not be 45xc2x0, 90xc2x0, etc.
In FIG. 2B1 the straight position is shown again, while FIG. 2B2 shows the straight lateral position which allows the wheelchair to travel straight sideways to the right or the left while the rider remains facing forward. To get to the straight lateral position from the straight position, the right drivewheel 6(a) rotates 90xc2x0 clockwise and the left drivewheel 6(b) rotates 90xc2x0 counterclockwise. FIG. 2C1 shows the straight position, while FIG. 2C2 shows the steered lateral position which allows the wheelchair to travel sideways to the right or left while being controllably steered to alter its course in that direction. To get to the straight lateral position from the straight position, the right drivewheel 6(a) rotates 90xc2x0 clockwise and the left drivewheel 6(b) rotates 90xc2x0 clockwise.
In using the prior art ""038 wheelchair, use of the straight lateral position shown at FIG. 2B2 can become difficult to control once the wheelchair is in straight horizontal motion. This lack of control necessitates that only the steered lateral position shown at FIG. 2C2 is used for both straight and curved horizontal movement.
However, this simplification of using only three essential positionsxe2x80x94straight, rotation, and (steered) lateralxe2x80x94makes certain common sequences of wheelchair movements unwieldy and particularly wasteful of limited battery power. For example, as shown in FIGS. 3A-3C, a wheelchair may be traveling straight (FIG. 3A), rotate to face another direction (FIG. 3B), and then move laterally to the right or left (FIG. 3C). In this sequence of movements, the right drivewheel 6(b) first rotates 45xc2x0 clockwise and then rotates an additional 45xc2x0 clockwise. However, the left drivewheel 6(b) first rotates 45xe2x80x2 counter-clockwise and then rotates a full 135xc2x0 clockwise to reach the lateral position. This sudden change in rotation direction (from counter-clockwise to clockwise) as well as the large required change in rotation angle (135xc2x0) makes difficult the implementation of a simple economical rotation system because of the constant additional drain on battery power.
Accordingly, there is a need for a wheelchair chassis with drivewheels that do not require a sudden change in rotation direction or a large change in rotation angle when performing common sequences of movements.
Accordingly, it is an object of the present invention to provide a wheeled chassis having independently operable drivewheels that permit true and efficient multidirectional motion of the chassis on and along a ground surface.
It is a further object of the invention to provide a wheeled chassis with drivewheels that do not require a sudden change in rotation direction when performing common sequences of movements.
It is another object of the invention to provide a wheeled chassis with drivewheels that do not require a large change in rotation angle when performing common sequences of movements.
It is still another object of the invention to provide linkage and shifting systems for the drivewheels of a wheeled chassis.
The foregoing and other objects and advantageous features of the instant invention are achieved by the provision of a wheeled chassis having independently pivotable drivewheels for multidirectional motion attached to a generally rectangular frame. The axis of rotation for one or more drivewheels is offset from the corner of the generally rectangular frame of the wheeled chassis, and the offset thus created produces stable, controlled, and efficient multidirectional motion.
One preferred embodiment of the present invention comprises a substantially rectangular frame having front, rear, first, and second sides; at least one free-spinning wheel rotatably attached proximate to the front side of the frame; a rear drivewheel attached at a location on the first side of the frame by a kingpin which is secured in a vertical channel located at the first side location and has a substantially vertical axis about which the rear drivewheel may rotate; and an offset drivewheel attached at a location on the second side of the frame by a kingpin which is secured in a vertical channel located at the second side location and has a substantially vertical axis about which the offset drivewheel may rotate. The distance of the second side location from the front side of the frame is less than the distance of the first side location from the front side of the frame and the difference between said second and first side distances is the offset distance. The rear and offset drivewheels determine the direction of movement of the wheeled chassis and the offset distance between the drivewheels provides stability, control and efficiency to the movements of the wheeled chassis.
Another preferred embodiment of the present invention comprises a substantially rectangular frame having a front, rear, first, and second side; at least one free-spinning wheel rotatably attached proximate to the rear side of the frame; a wheeled support means attached proximate to the front side of the frame; a first drivewheel attached to a first offset location located on the first side a first offset distance away from the corner of the first and rear sides of said frame, where the first drivewheel is connected to the frame by a kingpin which is secured in a vertical channel located in the first offset location and has a substantially vertical axis about which the first drivewheel may rotate; a second drivewheel attached to a second offset location located on the second side a second offset distance away from the corner of the second and rear sides of said frame, where the second drivewheel is connected to the frame by a kingpin which is secured in a vertical channel located in the second offset location and has a substantially vertical axis about which the second drivewheel may rotate.
Inventive exemplary shifting systems for rotating the drivewheels into preferred positions for travel are also described.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.